Control system



Feb. 27, 1962 K, H. SUEKER ETAL CONTROL SYSTEM Filed Feb. 12. 1958 INVENTORS Keith H. Sueker and Ronald C. Blockmond.

I v 34 0 0 E as 5 32 N l 0 o o 2 72" 45 44 a 42 LK 43 19 I Ll MIA 5-9 22 23 L '|'|'r- I, 24 g 2 2s 21 ww L Heater Healer Heater Heater 9| 92 95 94 WITNESSES ATTORNEY United States Patent ()fifice 3,023,355 Patented Feb. 27, 1962 3,023,356 CGNTRQL SYSTEM Keith H. Suelrer, Pittsburgh, and Ronald C. Blaclnnond, Allison Park, Pan, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 12, 1958, Ser. No. 714,785 6 Claims. (Cl. 32369) This invention relates in general to control systems and in particular to temperature control systems utilizing static elements.

Temperature control systems have many applications today. A system having reliability, ruggedness and maintenance-free operation is required in a nurnber of these applications. For example, in the process of making stretch nylon, a heat set is given to the twisted nylon yarn. This is accomplished by pulling the yarn through a small tube in an electrical heater unit raising the temperature of the yarn to nearly the melting point of nylon.

In the present invention the power to the heater units is supplied by magnetic amplifier, saturable reactor control. The magnetic amplifier output, which supplies the control winding of a saturable control, is controlled by balancing the resistance of a plurality of sensing resistors or impedances against the resistance of a fixed reference resistor or impedance. The sensing resistors and the fixed resistor control the current into oppositely polarized control windings of the magnetic amplifier, such that a decrease in sensing resistor resistance will cause greater current in the control winding to which it is connected and, this in turn, causes greater output of the magnetic amplifier and saturable reactor. Similarly, an increase in resistance lowers system output. The level of the system output and, thus, heater temperature is adjusted by varying the value of the fixed resistance or impedance. The sensing impedances or resistors may consist of positive temperature coefficient resistance wire wound around each heater element in the plurality of heater units. The fixed reference resistance is composed of material having a low temperature coefiicient so that its resistance does not materially change with ambient conditions. Thus, an increase or decrease in heater temperature causes an increase or decrease, respectively, in the sensing circuit resistance.

It is an object of this invention to provide an improved temperature control system.

It is another object of this invention to provide an im proved temperature control system utilizing static, reliable, rugged and maintenance-free elements.

It is still another object of this invention to provide an improved temperature control system which is relatively insensitive to ambient conditions, has a rapid rise of temperature to control temperature, and is simple in design.

Further objects of this invention will become apparent when the following description is taken in conjunction with the accompanying drawing. In the drawing, for illustrative purposes only, is shown a preferred embodiment of the invention. In said drawing the manner in which the windings have been wound upon the saturable magnetic cores has been denoted by the polarity dot convention. Thus current flowing into the polarity dot end of a winding will drive the associated core toward positive saturation. Current flowing out of the polarity dot end of a winding will drive the associated core away from positive saturation.

Referring to the drawing there is shown a temperature control system embodying the teachings of this invention which comprises in general a magnetic amplifier 56, a saturable reactor 79, an output transformer 89, and a regulating or control circuit 20.

The magnetic amplifier 50 comprises a pair of reactors 30 and 40. The reactor 30 comprises a saturable magnetic core 31 having inductively disposed thereon an output winding 32, a control winding 33 and a control winding 34. The reactor 40 comprises a saturable magnetic core 41 having inductively disposed thereon an output winding 42, a control winding 43 and a control winding 44. The output windings 32 and 42 are connected through a pair of self-saturating rectifiers 36 and 46, re spectively, and an alternating-current voltage source It) across the input of a full-wave rectifier 60 in what is known to those skilled in the art as a doubler arrangement.

The saturable reactor 70-comprises a saturable magnetic core 71 having inductively disposed thereon a control winding 73 and a load winding 75. The saturable reactor 70 also comprises a saturable magnetic core 72 having inductively disposed thereon a control winding 74 and a load winding 76. The control windings 73 and 74 are serially connected across the output of the full-wave rectifier 60. The load windings 75 and 76 are serially connected with a primary widing of the transformer 80 to an alternating-current voltage power source 79. The secondary winding of the transformer 80 is connected to supply a plurality of heating elements 91, 92, 93 and 94, which is the load for the system.

The regulating circuit 20 comprises two parallel branches connected to a source of direct-current voltage 21. A first parallel branch includes a current limiting resistance 23, a potentiometer 22, the control winding 43 and the control winding 33 all connected in series circuit relation ship. The sec-0nd parallel branch connected to the directcurrent source 21 comprises the plurality of sensing resistors 24, 25, 26 and 27 connected in series circuit relationship with the control windings 34 and 44 of the magnetic amplifier 50.

The operation of the magnetic amplifier 50 is well known to those skilled in the art. However, a brief summary is as follows. The alternating-current voltage 10 alternately drives the saturable magnetic cores 31 and 41 toward positive saturation by the application of a current through the self-saturating rectifiers 36 and 46 to the output windings 32 and 42, respectively. If the flux level in the saturable magnetic cores 31 and 41 is not reset away from positive saturation by the control windings 33 and 43, respectively, the magnetic amplifier 50 will deliver an output to the full-wave rectifier 60 after the cores 31 and 41 have been driven to positive saturation.

The current 1,, as designated in the drawing, will tend to drive the cores 31 and 41 away from positive saturation and thus limit the output of the magnetic amplifier 50. The current I as designated in the drawing, will drive the cores 31 and 41 toward positive saturation by flowing through the control windings 34 and 44, respectively, and thus increase the output of magnetic amplifier 5i).

The operation of the saturable reactor 70 is also well known to those skilled in the art. The direct-current voltage received from the full-wave rectifier 60 will regulate the flux level of the saturable magnetic cores 71 and 72. The flux level thus set in the cores 71 and 72 will determine the amount of output received from the alternating-current voltage power source 79 through the load windings 75 and 75 to the primary winding of the output transformer 80. The output transformer 30 couples or delivers an alternating-current voltage to the heater elements 91 and 92, 93 and 94.

The constant direct-current voltage 21, with polarity as shown in the drawing, is applied across the parallel circuits hereinbefore described causing the currents L, and l to flow in the two parallel branches. The value of the potentiometer 22 plus the value of the resistance 23 is set for the desired resistance to be attained by the sum of the plurality of sensing resistors 24, 25, 26 and 27. When the heating loads of the elements 91, 92, 93 and 94- are cold, the current I will be much greater than the current I since the resistance of the sensing resistors is much smaller. Therefore, the current through the control windings 34- and 44 will be much larger than the current through the control windings 33 and 43 and the magnetic amplifier 5% will be delivering a full output to the control windings 73 and 74 of the saturable reactor 7%. Thus the saturable reactor 7% will have a fu l output through the transformer 3t) to the heating elements 91, 92, 9'3 and 94.

As the heating elements approach the desired temperature, the resistance of the sensing resistors 24, 25, 26 and 27 rises and the current I decreases below the current 1,. Therefore the magnetic amplifier 56 tends to decrease its output, thus, decreasing the output of the saturable reactor 70. The temperature of the heater elements 91, 92, 93 and 94 will then stabilize around the value which tends to balance the currents I and 1 In the drawing a pair of bias windings and are shown inductively disposed upon the cores 31 and 41, respectively. Their use is optional. However, usually the magnetic amplifier 56 need on y be biased to a fixed or predetermined operating point or output level if the gain of the system is low.

Any temperature within the operational range can be obtained by varying the resistance of the potentiometer 22. Accuracy for the system is attained through the high sensitivity of the magnetic amplifier which may be made to produce a complete on-off swing in amplifier output for a small change in temperature. Stability for the system is insured by the long time constant in the heating load, which reduces the control to essentially a first order system.

A temperature control system has been disclosed which has a rapid rise of temperature to the control temperature desired, is relatively insensitive to ambient conditions, and is simple in design and construction. The system is inherently reliable, and rugged and allows a maintenancefree operation. Any magnetic amplifier giving the desired output, in response to the regulating circuit shown, may be utilized even though a doubler circuit connection has been shown in the drawing. Although positive temperature coeflicient resistors mentioned for the resistances 24, 25, 26 and .7 were used as examples, any sensing element having the desired electrical impedance variance in response to temperature change or thermal conditions of the load and allowing the proper current fio-w therethrough may be used, e. g., negative temperature coefficient elements. If negative temperature coefficient resistors are used, of course, the polarity of the control windings must be reversed.

In conclusion, it is pointed out that while the illustrated example constitutes a practical embodiment of our invention, we do not limit ourselves to the exact details shown, since modifications of the same may be varied without departing from the spirit and scope of this invention.

We claim as our invention:

1. In a control system, in combination, a magnetic amplifier having first and second control winding means inductively disposed upon saturable means; regulating circuit means; saturable reactor means; means connecting an output of said magnetic amplifier to control an output of said saturable reactor means; and means connecting the output of said saturable reactor means to a load; said regulating circuit having first and second parallel branches connected to a direct-current voltage source; said first parallel branch comprising sensing means connected to regulate current flow in said first control winding means of said magnetic amplifier; said sensing means having a varying impedance characteristic in response to varying thermal conditions of said lead; said second parallel 4. branch comprising reference impedance means serially connected with said second control winding means.

2. In a control system, in combination, a magnetic amplifier having first and second control winding means inductively disposed upon saturable means; regulating circuit means; saturable reactor means, means connecting an output of said magnetic amplifier to control an output of said saturable reactor means; and means connecting the output of said saturable reactor means to a load; said regulating circuit having first and second parallel branches connected to a constant direct-current voltage source; said first parallel branch comprising sensing means connected to regulate current flow in said first control winding means of said magnetic amplifier; said sensing means having a varying impedance characteristic in response to varying thermal conditions of said load; said second parallel branch comprising reference impedance means serially connected with said second control winding means.

3. In a control system, in combination, a magnetic amplifier having first and second control winding means inductively disposed upon saturable means; regulating circuit means; saturable reactor means; means connecting an output of said magnetic amplifier to control an output of said saturable reactor means; and means connecting the output of said saturable reactor means to a load; said regulating circuit having first and second parallel branches connected to a constant direct-current voltage source; said first parallel branch comprising sensing means connected to regulate current flow in said first control winding means of said magnetic amplifier; said sensing means having a varying impedance characteristic in response to varying thermal conditions of said load; said second parallel branch comprising reference impedance means serially connected with said second control winding means; said reference impedance means having a low temperature coeflicient of resistance.

4. In a control system, in combination, a magnetic amplifier having first and second control winding means inductively disposed upon saturable means; regulating circuit means; saturable reactor means; means connecting an output of said magnetic amplifier to control an output of said saturable reactor means; and means connecting the output of said saturable reactor means to a load; said reg ulating circuit having first and second parallel branches connecting to a constant direct-current voltage source; said first parallel branch comprising sensing means connected to remilate current flow in said first control Winding means of said magnetic amplifier; said sensing means having a varying impedance characteristic in response to varying thermal conditions of said load; said second parallel branch comprising reference impedance means serially connected with said second control winding means; said reference impedance means having a low temperature coefficient of resistance; said first and second control winding means being oppositely polarized.

5. In a control system, in combination, a magnetic amplifier having first and second control winding means inductively disposed upon saturable means; said magnetic amplifier having bias winding means inductively disposed upon said saturable means to bias said magnetic amplifier to a predetermined output level; regulating circuit means; saturable reactor means; means connecting said output of said magnetic amplifier to control an output of said saturable reactor means; and means connecting the output of said saturable reactor means to a load; said regulating circuit having first and second parallel branches connected to a constant direct-current voltage source; said first parallel branch comprising sensing means connected to regulate current flow in said first control winding means of said magnetic amplifier; said sensing means having a varying impedance characteristic in response to varying thermal conditions of said load; said second parallel branch comprising reference impedance means serially connected with said second control winding means; said reference impedance means having a low temperature coefficient of resistance; said first and second control winding means being oppositely polarized.

6. In a control system, in combination, a magnetic amplifier having first and second control Winding means inductively disposed upon saturable means; regulating circuit means; saturable reactor means; means connecting an output of said magnetic amplifier to control an output of said saturable reactor means; and means connecting the output of said saturable reactor means to a load; said regulating circuit having first and second parallel branches connected to a direct-current voltage source; said first parallel branch comprising sensing means connected to regulate current flow in said first control winding means of said magnetic amplifier; said sensing means having a varying impedance characteristic in response to varying thermal conditions of said load; said second parallel branch comprising reference impedance means serially connected with said second control Winding means; said first and second control winding means being oppositely polarized.

References Cited in the file of this patent UNITED STATES PATENTS 2,522,826 Hooven Sept. 19, 1950 2,568,411 Reed Sept. 18, 1951 2,608,635 Merohon Aug. 26, 1952 2,706,764 Mitchell Apr. 19, 1955 2,706,765 Lengvenis Apr. 19, 1955 2,733,404 Ogle June 31, 1956 

